Band-dependent superconducting gap in SrFe2(As0.65P0.35)2 studied by angle-resolved photoemission spectroscopy

H Suzuki; T Kobayashi; S Miyasaka; K Okazaki; T Yoshida; M Horio; L C C Ambolode 2nd; Y Ota; H Yamamoto; S Shin; M Hashimoto; D H Lu; Z-X Shen; S Tajima; A Fujimori

doi:10.1038/s41598-019-52887-y

Band-dependent superconducting gap in SrFe₂(As_0.65P_0.35)₂ studied by angle-resolved photoemission spectroscopy

Sci Rep. 2019 Nov 11;9(1):16418. doi: 10.1038/s41598-019-52887-y.

Authors

H Suzuki¹, T Kobayashi², S Miyasaka^{2

3}, K Okazaki^{4

5}, T Yoshida^{4

3}, M Horio⁴, L C C Ambolode 2nd⁴, Y Ota⁵, H Yamamoto⁵, S Shin^{3

5}, M Hashimoto⁶, D H Lu⁶, Z-X Shen⁶, S Tajima^{2

3}, A Fujimori^{7

8}

Affiliations

¹ Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan. [email protected].
² Department of Physics, Osaka University, Toyonaka, Osaka, 560-8531, Japan.
³ JST, Transformative Research-Project on Iron Pnictides (TRIP), Chiyoda, Tokyo, 102-0075, Japan.
⁴ Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan.
⁵ Institute for Solid State Physics (ISSP), University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
⁶ Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California, 94305, USA.
⁷ Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan. [email protected].
⁸ JST, Transformative Research-Project on Iron Pnictides (TRIP), Chiyoda, Tokyo, 102-0075, Japan. [email protected].

Abstract

The isovalent-substituted iron pnictide compound SrFe₂(As_1-xP_x)₂ exhibits multiple evidence for nodal superconductivity via various experimental probes, such as the penetration depth, nuclear magnetic resonance and specific heat measurements. The direct identification of the nodal superconducting (SC) gap structure is challenging, partly because the presence of nodes is not protected by symmetry but instead caused by an accidental sign change of the order parameter, and also because of the three-dimensionality of the electronic structure. We have studied the SC gaps of SrFe₂(As_0.65P_0.35)₂ in three-dimensional momentum space by synchrotron and laser-based angle-resolved photoemission spectroscopy. The three hole Fermi surfaces (FSs) at the zone center have SC gaps with different magnitudes, whereas the SC gaps of the electron FSs at the zone corner are almost isotropic and k_z-independent. As a possible nodal SC gap structure, we propose that the SC gap of the outer hole FS changes sign around the Z-X [(0, 0, 2π) - (π, π, 2π)] direction.